It is known for large or heavy vehicles such as buses, coaches and heavy goods vehicles (HGVs) to be provided with brake actuators having a service brake for deceleration when the vehicle is in motion and a parking brake to hold the vehicle stationary. The service brake is usually pneumatically actuated, and the parking brake is usually spring-actuated, with a pneumatic system being provided to maintain the parking brake in an unactuated condition when it is not required.
In some such vehicles, notably trailers for HGVs, the parking brake also acts as an emergency brake which can be used to decelerate and stop the vehicle automatically in the event of failure of the service brake, for example if the supply of compressed air to the service brake is interrupted or disconnected. In order to do this, a quick release valve (QRV) is provided which allows the rapid release of air from the parking brake system to actuate the parking brake. One such quick release valve is disclosed in the applicants' co-pending UK patent application, no. 0415324.3, and includes a moveable disc or diaphragm with a resiliently deformable skirt disposed between an upper inlet port and a lower exhaust port, with an outlet port being provided to one side of and beneath the exhaust valve. When the parking brake is not required, compressed air is supplied through the inlet port of the QRV, creating pressure on the diaphragm such that it seals the exhaust port, whilst the skirt flexes to allow the compressed air to pass from the inlet port to the outlet port. When the parking brake is required, for example if the vehicle is parked, or if the supply of compressed air has been disconnected, the disc moves to seal the inlet port, allowing air to flow from the outlet port to the exhaust port, thus causing the parking brake to be actuated.
The applicants have found that, whilst QRVs of this type are generally effective, there can be a delay, sometimes of up to fifteen seconds, between the supply of compressed air being disconnected from the inlet port and the parking brake being actuated, as the moveable disc and resiliently deformable skirt sometimes move in an unpredictable fashion, leaving the exhaust outlet of the QRV sealed. Although this is not a concern when the vehicle is stationary, in an emergency situation such a delay may be dangerous.
Thus, it is an object of the present invention to provide a quick release valve which eliminates, or at least reduces, this delay.